1. Field of the Invention
The present invention relates to a die bonding apparatus for die bonding, for example, a semiconductor chip to a substrate.
2. Description of the Related Art
In various electronic apparatuses, chips which are semiconductor devices are mounted as component parts. During the operation of a chip, the chip generates heat by being energized, and its temperature rises; however, there is a problem in that if the temperature of the chip rises excessively, its operation becomes unstable. To solve this problem, the chip is soldered, i.e., die bonded, to a substrate which also serves as a heat sink. The chip is die bonded to the substrate whereby the heat generated during the operation of the chip is radiated through the substrate. Therefore, the excessive temperature rise of the chip is suppressed, thereby maintaining the stable operation of the chip.
FIG. 11 is a cross-sectional view illustrating in a simplified form the state in which a chip 1 is die bonded to a substrate 2. The die bonding of the chip 1 with respect to the substrate 2 is generally effected as follows: Foil-like solder 3 is supplied to the surface of the substrate 2 to be die bonded, and the chip 1 is disposed on the side of the solder 3 which is opposite to a side of the solder 3 facing the substrate 2, such that the surface of the chip 1 to be die bonded is in contact with the solder 3. Namely, the chip 1, the solder 3, and the substrate 2 are arranged in that order such that the solder 3 is interposed between the chip 1 and the substrate 2. The chip 1 and the substrate 2 with the solder 3 interposed therebetween are loaded in, for example, a heat treatment furnace, and are heated to a temperature above the melting point of the solder 3. After the solder 3 melts and is filled in the gap between the chip 1 and the substrate 2, the chip 1, the substrate 2, and the solder 3 are cooled down to room temperature, thereby completing die bonding.
There are cases where bubbles 4 are produced in the solder 3 bonding the chip 1 and the substrate 2 owing to the entrainment of air or an atmospheric gas which is present in the heat treatment furnace or by an organic gas evaporating from the chip and the substrate which are die bonded. Since the portions of the bubbles 4 formed in the solder 3 are cavities, the thermal conductivity is extremely low in these portions as compared with the solder 4. The plurality of zigzag lines 5 in FIG. 11 schematically show the state in which the heat generated in the chip 1 during operation passes through the solder 3 and the substrate 2 and is radiated. The heat generated in the chip 1 is conducted toward the substrate 2, as indicated by the zigzag lines 5, but the heat is substantially not conducted at the portions of the bubbles 4 where the thermal conductivity is low. Accordingly, as for the heat generated in the chip 1, if the bubble 4 are present in the solder 3, the thermal conductivity declines appreciably at the portions of the bubbles 4, so that smooth heat conduction to the substrate 2 is hampered, and the temperature of the chip 1 rises undesirably.
In addition, if the bubbles 4 are present in the solder 3, the area of bonding between the chip 1 and the substrate 2 decreases, so that the bonding surface is subjected to thermal stresses occurring due to the repetition of the temperature rise and cooling during the operation and non-operation of the chip 1, thereby promoting the deterioration of the bonding surface. For this reason, it is necessary to suppress the occurrence of the bubbles 4 in the solder 3 at the time of die bonding the chip 1 and the substrate 2.
In the related art for suppressing the occurrence of bubbles in the solder at the time of die bonding, for instance, there is a method for controlling the temperature profile of the heat treatment furnace for melting and solidifying the solder. By controlling the temperature profile of the heat treatment furnace, a gas which causes the formation of bubbles is sufficiently removed from the solder during the melting and solidification of the solder, thereby suppressing the formation of the bubbles. However, with the method for controlling the temperature profile, there are problems in that it is impossible to obtain a noticeable effect in suppressing the occurrence of bubbles, that the temperature profile changes depending on the types of chips and substrates, and that time is required until the completion of die bonding, resulting in a decline in the efficiency.
In addition, as another example in the related art for suppressing the occurrence of bubbles, JP-A-5-283449, for example, discloses a technique wherein solder is remelted, and bubbles in the solder are removed by imparting ultrasonic vibrations to the solder at the time of remelting. In this related art, however, since the solder subjected once to die bonded is remelted, there is a problem in that the number of processes increases, resulting in a decline in the production efficiency. In addition, since a device for imparting ultrasonic vibrations is required, there is a problem in that the apparatus becomes large in size and complex.
Furthermore, as other examples of the related art for suppressing the occurrence of bubbles, JP-A-63-76461 and JP-A-2-161736, for example, disclose techniques wherein grooves or holes are formed in the substrate, and a gas which causes the occurrence of bubbles is allowed to escape through the grooves or holes formed in the substrate, so as to suppress the occurrence of the bubbles. In these examples of the related art, however, since the grooves or holes are formed in the substrate, there is a problem in that the strength of the substrate declines. In addition, since the substrate must be formed in advance, there is a problem in that the number of working processes increases, resulting in a decline in the production efficiency.
An object of the invention is to provide a die bonding apparatus, which is capable of suppressing the occurrence of bubbles in solder with a simple construction.
According to a first aspect of the invention, there is provided a die bonding apparatus for die bonding at least two members, which are heated in a heat treatment furnace, the apparatus including a first member having a surface to be die bonded on which solder is disposed, a base portion for mounting the first member thereon in a predetermined position, a second member disposed in an inclined manner with respect to the first member and facing the solder disposed on the surface of the first member to be die bonded, and an inclination attenuating member for inclining and holding the second member with respect to the first member, wherein the inclination attenuating member attenuates an angle of inclination of the second member with respect to the first member in a state in which the solder is melted.
In accordance with the invention, the arrangement provided is such that inclination attenuating member is included which, in a state in which the solder is in an unmolten state, holds the second member by inclining it with respect to the first member, and which, in a state in which the solder is in a molten state, attenuates the angle of inclination of the second member with respect to the first member so as to die bond the second member and the first member. Consequently, the molten solder is filled between the first member and the second member while being consecutively pressurized by the second member from one end portion toward the other end portion of the solder. Accordingly, since the gas which causes the occurrence of bubbles is removed from the molten solder, it is possible to form a sound soldered portion in which bubbles are few.
According to a second aspect of the invention, the inclination attenuating member is a thermally fusing member having a melting point exceeding a melting point of the solder.
According to a third aspect of the invention, the thermally fusing member is another solder.
In accordance with the invention, the inclination attenuating member is formed by a thermally fusing member, e.g., another piece of solder, which melts upon being heated to a temperature exceeding the melting point of the solder. Since the thermally fusing member is a solid at a temperature below the melting point of the solder, the thermally fusing member is capable of holding the second member in an inclined manner with respect to the first member. Upon being heated to a temperature exceeding the melting point of the solder, the thermally fusing member gradually melts and its shape changes, so that the thermally fusing member is capable of attenuating the angle of inclination of the second member with respect to the first member. Thus the inclination attenuating member can be realized with such a simple construction in which the thermally fusing member is provided, and it is possible to form a sound soldered portion in which bubbles are few.
In addition, since a desired melting point can be obtained for the solder by adjusting its chemical composition, the melting points of the solder and another piece of solder serving as the inclination attenuating member can be respectively set to desired temperatures. Consequently, when heating is effected to a temperature exceeding the melting point of the solder, the other piece of solder can be melted, thereby making it possible to reliably exhibit the function of attenuating the angle of inclination of the second member with respect to the first member.
According to a fourth aspect of the invention the inclination attenuating member is a heat-shrinkable member, which shrinks in a state in which the heat-shrinkable member is heated to a temperature exceeding a melting point of the solder.
According to a fifth aspect of the invention, the inclination attenuating member is a heat-sublimating member, which sublimates in a state in which the heat-sublimating member is heated to a temperature exceeding a melting point of the solder.
In accordance with the invention, the inclination attenuating member is formed by a heat-shrinkable member or a heat-sublimating member. Since, at a temperature below the melting point of the solder, the heat-shrinkable member and the heat-sublimating member are solids and their initial shapes are maintained, the heat-shrinkable member and the heat-sublimating member are capable of holding the second member in an inclined manner with respect to the first member. Upon being heated to a temperature exceeding the melting point of the solder, the heat-shrinkable member undergoes thermal shrinkage and its volume is reduced, while the heat-sublimating member vaporizes and its volume is reduced, so that the angle of inclination xcex81 of the second member with respect to the first member can be gradually attenuated. Thus the attenuation of the angle of inclination of the second member with respect to the first member can be realized with such a simple construction in which the heat-shrinkable member or the heat-sublimating member is provided, and it is possible to form a sound soldered portion in which bubbles are few.
According to a sixth aspect of the invention the inclination attenuating member includes a supporting member one end portions of which abuts against the second member to support the second member and a driving member for driving the supporting member in a direction in which the one end portion of the supporting member abutting against the second member approaches the base portion in the state in which the solder is melted.
In accordance with the invention, the inclination attenuating member includes a supporting member for supporting the second member and driving member for driving the supporting member in a direction in which the supporting member approaches the base portion. Since the angle of inclination of the second member with respect to the first member is thus attenuated by the mechanical arrangement, it is possible to use the identical inclination attenuating member repeatedly, and the reproduction of operation can be ensured positively.
According to a seventh aspect of the invention, the inclination attenuating member includes a spring member provided on the base portion to support the second member and a compressing member for compressing the spring member in a direction in which one end portion of the spring member supporting the second member approaches the base portion in the state in which the solder is melted.
In accordance with the invention, the inclination attenuating member includes a spring member for supporting the second member and compressing member for compressing the spring member. Since the angle of inclination of the second member with respect to the first member is thus attenuated by the spring member and the compressing member, it is possible to use the identical inclination attenuating member repeatedly, and the reproduction of operation can be ensured positively.
According to an eighth aspect of the invention, there is provided a die bonding apparatus for die bonding at least two members, which are heated in a heat treatment furnace, the apparatus having a first member having a surface to be die bonded on which solder is disposed, a base portion for mounting the first member thereon in a predetermined position, a second member disposed in an inclined manner with respect to the first member and facing the solder disposed on the surface of the first member to be die bonded, and a magnetically attracting member for attracting the second member by a magnetic force.
In accordance with the invention, magnetically attracting member is provided for attracting the second member by a magnetic force. In the state in which the solder is melted, the angle of inclination of the second member with respect to the first member can be attenuated by the magnetic force of the magnetically attracting member. Thus the magnetically attracting member can be used repeatedly for the attenuation of the angle of inclination of the second member, and the reproduction of operation can be ensured reliably.
According to a ninth aspect of the invention, there is provided a die bonding apparatus for die bonding at least two members, which are heated in a heat treatment furnace, the apparatus having a first member having a surface to be die bonded on which solder is disposed, a base portion for mounting the first member thereon in a predetermined position, a second member disposed in an inclined manner with respect to the first member and facing the solder disposed on the surface of the first member to be die bonded, a pushing-up member one end portion of which abuts against a side of the first member, which is opposite to a side thereof where the solder is disposed, and a pushing-up driving member for driving the pushing-up member in a direction in which the one end portion abutting against the first member moves away from the base portion in a state in which the solder is melted.
In accordance with the invention, the die bonding apparatus includes a pushing-up member whose one end portion abuts against the first member and pushing-up driving member for driving the pushing-up member in a direction in which the pushing-up member moves away from the base portion, and the pushing-up member driven by the pushing-up driving member moves the first member toward the second member to die bond the first member and the second member. Since the first member is moved toward the second member with such a mechanical arrangement, the pushing-up member and the pushing-up driving member can be used repeatedly, and the reproduction of operation can be ensured reliably.
According to a tenth aspect of the invention, there is provided a die bonding apparatus for die bonding at least two members, which are heated in a heat treatment furnace, the apparatus having a first member having a surface to be die bonded, a second member facing the surface of the first member to be die bonded, having solder on a surface thereof facing the first member, and disposed in such a manner as to be inclined with respect to the first member, and a base portion for mounting the first member thereon in a predetermined position, wherein the base portions is formed an inclination holding portion thereon so as to abut against the second member and hold a state of inclination of the second member with respect to the first member.
In accordance with the invention, on the base portion for mounting the first member thereon in a predetermined position, an inclination holding portion is formed so as to abut against the second member and hold the state of inclination of the second member with respect to the first member. Thus the holding of the inclination of the second member with respect to the first member with such a simple construction in which the inclination holding portion is formed on the base portion. By making use of the wettability and surface tension of the solder which is provided on the surface of the second member to be die bonded and which is in a molten state upon heating, the first member is gradually attracted toward the second member side, thereby making it possible to remove from the solder the gas which causes the occurrence of bubbles. Hence, it is possible to form a sound soldered portion in which bubbles are few.
According to an eleventh aspect of the invention, a die bonding apparatus for die bonding at least two members, which are heated in a heat treatment furnace, the apparatus having a first member having a surface to be die bonded on which solder is disposed, a second member disposed to face the first member in a state in which the solder disposed on the surface of the first member to be die bonded is interposed therebetween, a base portion for mounting the first member thereon in a predetermined position, wherein the base portion has a temperature distribution so that a temperature of a vicinity of a central portion in a predetermined direction of the base portion is higher than that of a vicinity of an end portion of the base portion in a state in which heating is effected in the heat treatment furnace.
In accordance with the invention, in the base portion for mounting the first member thereon in a predetermined position, a temperature distribution is formed such that the temperature of a vicinity of a central portion in a predetermined direction of the base portion becomes higher than the temperature of a vicinity of an end portion of the base portion in a state in which heating is effected in the heat treatment furnace. Consequently, since the solder disposed on the surface of the first member to be die bonded consecutively melts, starting from a portion corresponding to the central portion of the base portion where the temperature is high toward a portion corresponding to an end portion of the base portion where the temperature is low. Therefore, the gas which causes the occurrence of bubbles is removed in the consecutively melting process, so that a sound soldered portion in which bubbles are few is formed.
According to a twelfth aspect of the invention, the base portion is formed so that the thickness of the vicinity of the central portion in the predetermined direction is smaller than that of the vicinity of the end portion.
In accordance with the invention, the base portion is formed such that the thickness of the vicinity of the central portion in the predetermined direction is smaller than the thickness of the vicinity of the end portion. Accordingly, since the quantity of heat in the central portion of the base portion becomes smaller than the quantity of heat in the end portion thereof, the temperature of the central portion rises earlier than that of the end portion. By virtue of such a simple construction in which the thickness of the central portion of the base portion is made smaller than the thickness of the end portion thereof, it is possible to realize a temperature distribution for setting the temperature of the central portion of the base portion higher than that of the end portion thereof.
According to a thirteenth aspect of the invention, a heat conducting member having a thermal conductivity exceeding the thermal conductivity of the base portion is provided on an outer side of the base portion in contact with the base portion.
In accordance with the invention, a heat conducting member having a thermal conductivity higher than the thermal conductivity of the base portion is provided in contact with the base portion. Since the quantity of heat transmitted to the base portion through the heat conducting member and thereby dissipated is small in the central portion of the base portion and is large in the end portion thereof, the temperature of the central portion rises earlier than that of the end portions in accordance with the heat balance. By virtue of such a simple construction in which the heat conducting member is provided which is in contact with the base portion and has a thermal conductivity higher than that of the base portion, it is possible to realize a temperature distribution for setting the temperature of the central portion of the base portion higher than that of the end portion thereof.